With many vehicle roofs on present day automotive vehicles, an outer metallic skin of the roof structure is too thin to offer adequate stability for fastening add-on components such as a roof rail, sometimes referred to as a “profile”, which will be required to support the loads associated with articles being transported on the roof rail. As a result, such add-on parts as roof rails are preferably mounted in areas of the roof structure where underlying reinforcing body structures such as frames, roof flanges or bars are located. The roof rails are supported on the outer body sheet metal on the outside but are anchored on the rigid body structure situated beneath it. However, due to manufacturing tolerances, the distance between the outer skin of the vehicle roof and the underlying structure which is situated further toward the inside of the vehicle, but which needs to be attached to in order to securely affix the roof rail to the outer body surface, is subject to dimensional fluctuations.
Fastening arrangements such as those disclosed in EP 0 950 569 B1 and EP 1 705 066 B1, which can compensate for certain tolerances in the distance between the outer skin and the structure arranged further toward the inside of the vehicle, are thus already known. For reliable fastening of the roof rail, the roof rail may be provided with a retaining foot, which can be passed through a mounting opening in the outer skin of the roof and is then attached to the body structure from the inside of the vehicle with the help of clamping means. A bolt having a screw can be used to act on a spreading sleeve in the retaining foot, and thus this arrangement may be used to compensate for the spacing tolerances between the outer skin and the underlying body structure.
With the fastening arrangement according to EP 0 950 569 B1, the add-on part (e.g., roof rail) is supported on the automotive body outer skin without prestress due to its construction unless the add-on part is acted upon by a prestressing force during the tightening of the screw connection from above, i.e., manually. However, this makes the assembly process more difficult because at the same time a pressure must be exerted from the outside onto the add-on part while the screw connection must be tightened from the inside. Therefore, two people must work together in practice to accomplish this assembly, one person applying a force to a portion of the add-on part from the outside while a person on the inside of the vehicle tightens the screw that clamps the add-on part to the vehicle roof.
However, the fastening arrangement according to EP 1 705 066 B1 is designed so that it can be mounted by one person alone while achieving a prestress of the add-on part against the vehicle body outer sheet metal. For this purpose, the end of the bolt on the outer end of the body end is designed as an enlarged retaining head which stretches a spring element between itself and the retaining foot. When the bolt is tightened, the spring element is compressed, with the result being a prestressing force of the add-on part on the outer skin of the vehicle. The prestress is an advantage, but the size of the stress depends to a great extent on the distance between the outer skin of the vehicle body and the body structure arranged between it. The greater this distance, the greater also the pressure of the add-on part on the outside of the vehicle body after assembly. An excessive pressure of the add-on part on the outer metal roof surface can cause a slight concave depression to become visible in the roof when the attachment is effected, and such a condition is highly undesirable from an aesthetic viewpoint.
Thus, one important consideration, which the present invention meets, is therefore to permit prestressing of the add-on part (roof rail) against the outside surface of the vehicle roof independently of the dimensional tolerances in the roof structure, while also permitting simple and convenient assembly operation to be carried out by a single individual.